Car crashes have killed 3x as many people in the US as all wars:

Sources:

The code below generates this plot:

Helper for:

1. U.S. Motor Vehicle Fatalities

Pull table from Wikipedia article: Motor vehicle deaths in U.S. by year

Clean data:

2. U.S. casualties of war

Pull table from Wikipedia article: United States military casualties of war

Clean data

Parse dates into start and end years, and numeric casualty ranges into lo and hi estimates

Use the low-end estimates, drop final "total" row

Approximate each war's deaths as being evenly spread over the years in which the war was waged:

3. Combine per-year car and war deaths

Fill in missing years, add cumulative sums

4. Plot